How plastic injection molding works? Ultimate Guide 2022

Feb 02, 2022

General working principle of plastic injection machine

How plastic injection molding works? The basic plastic injection molding machine structure has shown the functions of each part working together. These parts operate on a common working principle.

Raw plastic (Plastic) is put into the material storage compartment through a hopper. The plastic granules in the cavity melt by a heater. We keep it in a liquid state until it enters the mold cavity.

The process of injecting plastic into the mold is similar to using a needle. The motor generates force on the helical screw. The screw operates in a clockwise direction creating a large pressure that pushes the plastic to the valve.

What is injection mold clamping system?

The mold clamping system has the role of fixing the mold under the impact of huge pressure. And the cooling system will quickly cool the product to push it out of the mold to continue a new press.

How plastic injection molding works? All presses have a central operating system that controls the entire operation of the machine.

Detail working principle of Horizontal plastic injection machine

Horizontal plastic injection molding machine is one of the most advanced presses available today. This machine originates from Japan.

The improvements of plastic injection machine bring positivity in production. Productivity and quality of pressed products are guaranteed, diverse and durable.

Plastic injection molding machine has various sizes for large molds and small molds. However, the size difference is relevant to the working principle of the horizontal plastic injection molding machine.

The working principle of the plastic injection molding machine

As learned about the plastic injection machine in detail in the structure and general operating principle of the above content, basically, the JSW machine is nothing else. It also works on the same principle: “Heating – injection molding – cooling – ejecting the product from the mold”.


How plastic injection molding works?  Injection molding machine is the most important machinery equipment common in plastic injection processing. In this article, we take a closer look at the structure of the injection molding machine and the parameters of plastic injection molding.

Details of injection molding machine structure

In general, an ordinary injection molding machine consists of 5 systems:

  • injection molding support system
  • Furthermore, injection system
  • Moreover,  clamping system
  • Mold system and control system.

Injection molding support system

How plastic injection molding works? The injection molding support system consists of 4 subsystems, each with its own function.

Body: is the part that has the function of linking the systems of the plastic injection machine together

Electrical system: includes electrical cabinets and wires, providing power, helping the motor to operate. The electrical system needs to be scientifically designed. Moreover, it helps to ensure the safety of the operator.

Hydraulic system: composes of pump, valve, and pipe system, motor... is the place to generate resources for closing and opening the mold.

The cooling system comes with the function of cooling the mold by water or Ethylene Glycol solution. In addition, it helps the plastic material to harden into the desired shape before ejection. Moreover, it solidifies the plastic into a shape before the product is ejected from the mold.

Spray system of injection molding machine

The injection system melts the plastic material under the influence of temperature, maintains the temperature of the liquefied plastic, compresses and degass it during the injection of the plastic into the mold cavity as well as the shaping of the product.

The injection system comes of a:

  • plastic feed hopper
  • Moreover, a plastic container
  • Similarly, heating rings
  • a screw
  • Furthermore, a nozzle and a self-opening return unit

How plastic injection molding works? During operation, when the screw moves backward, the wedge-shaped barrier moves towards the nozzle. The molten plastic will flow in front of the screw head. The screw moves forward, vice versa.

Clamping system

Clamping system with mold opening and closing function helps to hold the mold firmly while waiting for cooling and opens to push the product out of the mold.

The clamping system is composed of the pusher assembly, the clamp assembly, the connecting rods, the movable plate and the fixed plate.

Plastic Injection Mold system

The mold system is a plastic product forming injection molding system consisting of a fixed half and a movable half. In which, the fixed part carries the mold cavity (female mold) and the movable part carries the mold core (male mold).

How plastic injection molding works? The mold system with a very complex structure, basically includes the following components:

Guide and positioning system: including guide pin, guide bearing, positioner, positioning ring...

The system of leading plastic into the mold cavity: including the nozzle silver, plastic channel, nozzle...

Product pushing system: including push pin, return pin, support pin, support pin bearing, push plate, retaining plate, support block...

Cooling system: including water lines, grooves, heat pipes, connectors (hollow shaft pipes, faucets)...

Plastic Injection Molding Exhaust system:

The control system is the operating system of the injection molding machine. Injection molding parameters such as temperature, pressure, injection molding speed, position of hydraulic system parts clearly display on the control panel.

How plastic injection molding works? The control system is the basis for the injection molding machine to perform operations during the entire pressing cycle.

Parameters of injection molding

Different types of plastic injection molding machines will have different injection molding processing parameters. Some common features in the parameters that the plastic injection machine operator should understand include:

Spray speed

The injection speed has a direct impact on the shape, determining the characteristic properties of the product. It is necessary to set the standard injection molding speed based on the characteristics of the plastic injection machine and the plastic product you want to form.

If the pressing speed is too high, it will make the product not aesthetically pleasing, glossy, surface blurred or seam floating...


If the injection molding speed is too low, it will cause the mold not to be filled, causing lack of material, shrinkage, deformation, and failure to meet the required size standards.

Injection pressure

How plastic injection molding works? Just like injection molding speed, injection pressure has an effect on the operation of the injection molding machine and on the characteristics of the formed product.

If the injection molding pressure k adjusts reasonably, it will affect the quality and aesthetics of the formed product. Usually, high injection pressure is common in the production of parts that require thin walls and high pressure is common in the case of thick product walls.

Press area of injection molding

Products with different technical requirements require different injection molding areas. The pressing area clearly defines and the setting is reasonable during the whole injection molding process.

Injection area is an injection molding machine parameter that can affect the clamping force, mold size and technical parameters of the plastic injection machine.